Can anyone point me in the direction of a simple but reliable electronic load that can sink 0~20A on up to +12VDC. I have a design from Elecktor that looks promising if overly complicated. (I won't post it because it cost me money to obtain and it seems wrong to make it publicly available).

Here is a schematic of one I use, the transistor is mounted on a large heatsink. The transistor Q1 can use a 2n6284, or on occasions I have used n-channel mosfets. The size of the heat sink is important. The collector of the transistor is also connected to the+ of the DC source to be tested. I use this for testing current limit of power supplys discharging batteries. It is a constant current load.